Class 9 · ScienceNCERT 2026 Revised Syllabus
Chapter 5: Exploring Mixtures and their Separation (0906CH05)
Exploration · Solutions, colloids, suspensions and separation techniques.
Chapter code: 0906ch05 · Book: Exploration · Class 9 Science
Find complete NCERT solutions for Class 9 Science, Exploration Chapter 5. Every question has a clear, step-by-step answer for chapter code 0906CH05.
Pause and Ponder(10 questions)
1
A talcum powder contains 4% m/m zinc oxide. How much zinc oxide is in 300 g of talcum powder?
School Level Solution
Ans.
Mass of ZnO = (4/100) × 300 = 12 g
2
Two tablespoons (15 mL each) of orange juice concentrate mixed with water to make 150 mL. What is % v/v of concentrate?
School Level Solution
Ans.
Volume of concentrate = 2×15 = 30 mL; Total volume = 150 mL
% v/v = (30/150) × 100 = 20% v/v
% v/v = (30/150) × 100 = 20% v/v
3
Vinegar = 5% v/v acetic acid. How would you make vinegar from glacial (100%) acetic acid?
School Level Solution
Ans.
Take 5 mL of glacial acetic acid. Slowly add 95 mL of distilled water while stirring. Final solution = 100 mL of 5% v/v vinegar. (Always add acid to water — never water to acid.)
4
Equal masses of hot saturated solutions of A and B are cooled from 80°C to 60°C. Which deposits more solid?
School Level Solution
Ans.
The amount of solid deposited equals the decrease in solubility × mass of solvent. The compound with a steeper solubility curve between 80°C and 60°C has greater decrease in solubility → deposits more crystals.
5
Will the size of common salt crystals change if rate of evaporation is increased or decreased?
School Level Solution
Ans.
At faster evaporation: salt crystallises rapidly → many small crystals form simultaneously. At slower evaporation: gradual crystallisation → fewer, larger, well-shaped crystals. Rate of evaporation controls nucleation and crystal growth.
6
State True/False: (i) Salt separated by evaporation or distillation; (ii) Distillation works for same boiling point; (iii) Solvent level should be above sample spot; (iv) Evaporation and crystallization are same.
School Level Solution
Ans.
(i) True — both evaporation and distillation can separate salt from water. (ii) False — distillation works for liquids with different boiling points. (iii) False — solvent level must be below the sample spot (chromatography). (iv) False — evaporation removes solvent only; crystallisation controls cooling rate to form pure crystals.
7
Why do immiscible liquids form two separate layers in a separating funnel?
School Level Solution
Ans.
Immiscible liquids have different densities and dissimilar intermolecular forces. Denser liquid settles below; lighter floats on top. A separating funnel exploits this to drain them separately.
8
Is sublimation different from evaporation? Justify.
School Level Solution
Ans.
Yes, they differ. Evaporation: liquid → gas (at any temperature, from surface). Sublimation: solid → gas directly (no liquid intermediate) — e.g., iodine, naphthalene, camphor.
9
Clouds are made of tiny water droplets or ice crystals in air. What type of mixture are clouds?
School Level Solution
Ans.
Clouds are colloids (aerosols): tiny water droplets (1–1000 nm) dispersed in air. They show the Tyndall effect, do not settle quickly, and cannot be separated by filtration.
10
Why do cities with a lot of smoke and dust look hazy?
School Level Solution
Ans.
Smoke and dust particles form a colloidal system in air. These particles scatter light — the Tyndall effect — making the sky look hazy and opaque. Scattering reduces direct transmission of sunlight, limiting visibility.
Activities — How to Do(5 questions)
1
Activity 5.1 (three mixtures): Group A stirs salt in water, Group B chalk powder in water, Group C milk drops in water. Check visibility, shine a laser through each, leave undisturbed, then filter. Are these the same kind of mixture?
School Level Solution
Ans.
A (salt): particles invisible, no laser path, nothing on filter → true solution. B (chalk): particles visible, settle down, residue on filter → suspension. C (milk): invisible but shows a laser path (Tyndall effect), no residue → colloid.
2
Activity 5.3 (prepare crystals): dissolve copper sulphate in warm water with a drop of dilute sulphuric acid till saturated, filter hot, cool undisturbed, then filter and dry the crystals. What should you get, and what precautions apply?
School Level Solution
Ans.
Saturate warm water with copper sulphate (teacher adds the acid drop) → filter hot to remove impurities → cool slowly without disturbing → large, shiny blue crystals separate; rinse with cold water and dry. Precautions: do not touch chemicals; teacher handles acid and heating.
3
Activity 5.5 (paper chromatography): draw a pencil line 2 cm from the bottom of a paper strip, put a black ink spot on it, dip the strip in water (level below the spot) and watch. What do you notice and infer?
School Level Solution
Ans.
As water rises, the single black spot separates into different colour bands. Inference: black sketch-pen ink is a mixture of dyes that travel at different speeds on paper — the basis of chromatography as a separation technique.
4
Activity 5.6 (separating funnel): pour 5 mL mustard oil and 20 mL water into a separating funnel and let it stand. Which layer is which, and how do you collect them separately?
School Level Solution
Ans.
On standing, yellow oil forms the upper layer (less dense, immiscible) and water the lower layer. Open the stopcock slowly to run the water out first; close it as the boundary arrives, discard the mixed drops, then collect the oil separately.
5
Activity 5.7 (camphor sublimation): heat crushed camphor–sand mixture in a china dish covered with an inverted cotton-plugged funnel. What deposits where, and what does it prove?
School Level Solution
Ans.
On gentle heating, camphor sublimes (solid → vapour) and re-deposits as white solid on the cool funnel walls; sand stays in the dish. This proves sublimation separates a sublimable solid from a non-sublimable one without any liquid stage.